Are Soft Gamma-ray Repeaters (SGRs) 'Magnetars'?

Abstract

Soft Gamma-ray repeaters (SGRs) are among the most powerful Galactic sources of high energy radiation. These objects are even powerful enough to influence processes occurring in the near Earth environment. In the last few years X-ray observations with the Rossi X-ray Timing Explorer (RXTE) have provided us with a new understanding of SGRs. RXTE was instrumental in the discovery that SGRs are rapidly slowing X-ray pulsars and is still providing continued monitoring of their pulse periods. SGR bursts have now been observed with unprecedented sensitivity. I will review the current status of our knowledge of SGRs based on these recent X-ray observations and discuss their implications for models of SGRs, including the now substantial evidence that these objects are highly magnetized neutron stars or 'magnetars'. I will also describe recent spectral studies of SGR bursts which have revealed several new phenomena, including a burst with strong spectral evolution and evidence for a 6.4 keV emission line.